ntoskrnl.exe on vista..

Recently, using a vista PC which was bought as a vista pc, when I turn it on it says ntsokrnl.exe is missing/corrupt, and to reinstall the file. (however have been told that this is an XP file and isn't part of vista).

I tried going through dell support but they couldn't help.
When I put in the operating disk, it gave options of install vista, or to repair, so not wanting to lose files I tried to repair, and under system recovery options it couldn't find any operating system to repair, so I pressed next anyway, and start up repair didn't repair it, and system restore didn't even work.

Any ideas? Really don't want to lose data as got important files on there.

thanks

 

another thing, when it can't find any operating system, there's an option to load drivers. under this, I can see all my files etc under the F:\ but the C:\ appears to be completely empty and unformatted. Seems strange.

All I want to do is get the files I need off the computer, and then can replace the hard drive if needed, as it is under guarentee.

THanks